The present disclosure relates generally to radio communication systems. In typical radio communication systems, various subscribers communicate with one another either in a direct mode or an infrastructure mode transmitting voice, video, or other data (generally “data”) on working channels, which are predetermined frequencies and timeslots. The working channels can be random access channels which can be different depending on the message direction, e.g., an inbound (or uplink) channel is used for communications from the subscriber to the base station and an outbound (or downlink) channel is used for communications from the base station or repeater to the subscriber. When a subscriber wishes to transmit data to other subscribers, the subscriber first determines the status of the uplink channel—i.e., whether it is busy or idle. For example, in European Telecommunications Standards Institute Digital Mobile Radio (ETSI-DMR) systems, the downlink channel periodically transmits a CACH (Common Announcement Channel) burst that indicates the status of the uplink channel. Other types of radio communication systems such as Terrestrial Trunked Radio (TETRA), Project 25 (P25), Digital Mobile Radio (DMR), Land Mobile Radio (LMR), Motorola Trunked Radio, and the like may include similar mechanisms.
In many radio communication systems, the subscriber is required to monitor the uplink channel for an extended period of time prior to attempting to transmit data or the subscriber is required to request an opportunity to transmit data on the uplink channel. Once the subscriber determines that the uplink channel is idle, or after receiving a grant to transmit on the uplink channel, the subscriber may attempt to transmit the data to the base station or the repeater. If a large number of subscribers use the same uplink channel, multiple subscribers may attempt to transmit these requests at the same time, causing collisions between the requests. Base stations receiving multiple colliding messages at the same time typically do not respond to the messages as they mutually interfere with one another, causing each message to be eventually be retransmitted by the respective subscriber. Adding to this, communication systems also typically require a confirmation message be sent to the subscriber on the outbound channel to confirm receipt of the request from the subscriber. This increases the bandwidth usage on the outbound channel as well as further increasing the amount of time it takes to transmit the data from the subscriber on the uplink channel.
These problems have become increasingly problematic due to an increased desirability of tracking a locations of the subscribers, and doing so more often, using the Global Positioning System (GPS) or other location determination systems. As subscriber location information presents a heavy traffic load on a channel due to its frequent transmission and in order to minimize the impact that location data might have on other data traffic, such as voice traffic, the location data can be transmitted on a dedicated random access channel. As it is likely that the desirability for location tracking will only increase, and therefore the number of devices being tracked correspondingly increase, it is therefore desirable to provide a mechanism for location tracking using revert repeater channel(s) in which a number of dedicated revert channels and the amount of infrastructure employed, and thus an incurred cost, is reduced and in which the amount of time for channel access is minimized.
To improve GPS data throughput, a windowed data channel architecture has been introduced whereby each subscriber is assigned a window on a revert channel to transmit location data. For example, subscribers use a secondary (revert) channel to schedule and transmit updates to a repeater. The channel is structured to support non-contention based communication windows during which the location information is transmitted to the repeaters, i.e., a specific different window is assigned to each subscriber. This significantly improves the throughput of GPS or other location data in radio communication systems.
While the windowed data channel significantly improves GPS throughput, it requires each subscriber to request access for a data window from a windowed revert repeater channel in every roam. This is in addition to normal registration and is inefficient. Further, to accommodate a large number of subscribers in a GPS revert feature on the windowed revert repeater channel, a large number of windowed revert repeater channels is required.
Accordingly, there is a need for an improved method and system for transmitting periodic data such as location data on a windowed revert repeater channel in a radio communication system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.